chardie: You're making a huge mistake replacing the floorboards. Check the growth rings. There are 5 times as many on your old growth existing floor as there are on plantation pine replacements.

Depending on how exposed to the elements the porch floor is and how well it has been maintained, a porch floor could last 150 years, or it could last 50.

Also depends on the type of wood used, and if it was regularly painted with appropriate paint, how the snow was removed in winter, etc.

Believe me, I wish I could keep them. They are rotted. If they're original, I guess139 years is not a bad record.

It depends on how much weather is was subjected to.

A protected porch in a dry climate can last 100+ years. It will wear out from foot traffic before it rots.

Exposed wood in a wet/dry and freeze/thaw cycle is lucky if it lasts a couple of decades.